The present invention relates to a circuit arrangement for electronic data processing                having at least one non-volatile memory module for storing data to be protected against unauthorized access by means of en-/decryption;        having at least one memory module interface logic circuit assigned to the memory module        for addressing the memory module,        for writing the data to the memory module and        for reading the data from the memory module;        having at least one code Read Only Memory (ROM) module for storing at lease one ROM code; and        having at least one code ROM module interface logic circuit assigned to the code ROM module        for addressing the code ROM module and        for reading the ROM code from the code ROM module.        
The present invention further relates to a method of en-/decrypting data to be protected against unauthorized access in at least one non-volatile memory module.